1. Field of the Invention
The present invention relates to a wireless communication apparatus for selecting a suitable transfer route on a wireless network, and more specifically to such an apparatus, for setting a transfer route, for example, in a multi-hop wireless network such as a sensor network. The present invention also relates to a method and a computer program for implementing such an apparatus, as well as a wireless network for utilizing such an apparatuses.
2. Description of the Background Art
Conventionally, in a telecommunications network consisting of a plurality of communication terminals, various types of communication systems have been developed to communicate with other terminals not directly connected to the communication terminals by repeating transmission and receipt of packets between adjacent ones of those terminals.
In addition, in the network, a relaying terminal must select appropriate one of adjacent terminals which corresponds to the destination of a packet received for transmitting the packet to the terminal thus selected. This process is called route control, for which various schemes have been developed.
Generally, the route control selects a route with the minimum number of relaying hops. Thus, the selected route between two terminals may be often the same between upward and downward links.
In a wired network, because upward and downward communications are operated completely separately from each other, i.e. in a full duplex system, if the upward and downward communications use the same route, no problems would be caused.
By contrast, in wireless communications, upward and downward communications may not be frequently operated simultaneously, i.e. in a half-duplex system, and then the upward and downward communications may simultaneously take place to thus lower the efficiency of the communications.
Japanese patent laid-open publication No. 2006-157637 discloses a proposed system coping with the problems caused by the simultaneous occurrence of the upward and downward communications. In the proposed system, an inward gateway wireless station and an outward gateway wireless station are separately installed from each other so as to use all wireless communication paths as one-way routes.
However, when the route control scheme is adopted in a wireless multi-hop network, some problems may be caused as following.
Firstly, almost all wireless communication systems use the half-duplex communication so that the upward and downward communications cannot be performed simultaneously. If the paths of the upward and downward communications took the same route, wireless signals could interfere and collide with each other.
Secondly, in almost all communication systems, levels required for the delay and quantity of communications are asymmetric between the upward and downward communications. Therefore, if the upward and downward communications took the same route, the both communications would naturally be provided with the same quality. Thence, in an application in which the qualities required for the upward and downward communications may differ from each other, if a route is selected which has its quality suited to higher one, then the route may be provided in surplus.
Thirdly, the existing route control systems rely upon wired networks so as to be designed to select appropriate one of a limited variety of terminals physically connected. By contrast, in the wireless multi-hop network, especially sensor network, there are many terminals capable to communicate directly with devices existing in the periphery thereof, and moreover, the nature of wireless transmission provides communication connections apt to abruptly vary with respect to time. Thus, the existing route control scheme may thus fail to select an appropriate terminal.
Fourthly, the conventional route control scheme tends to cause communications to converge on a specific terminal, so that a lot of wireless signals may collide in the vicinity of such a specific terminal to thus lower the communication efficiency. Since the terminal on which the communications converges transfers a lot of packets, it consumes more electric power consumption than other terminals. Wireless multi-hop networks are designed on the assumption that the terminals operate with battery, and therefore the power consumption must be balanced between those terminals in order to extend the operating time of the entire network.
Although the system disclosed by the above-mentioned Japanese patent publication '637 can resolve the first problem, it needs to install at least two gateway wireless stations at separate positions, thereby causing a problem of increasing the cost.